Dexamethasone treatment did not exacerbate experimental Seneca Valley virus infection in nursery-age pigs

Authors: BUCKLEY, ALEXANDRA - Oak Ridge Institute For Science And Education (ORISE); MONTIEL, NESTOR - Oak Ridge Institute For Science And Education (ORISE); GUO, BAOQING - Iowa State University; KULSHRESHTHA, VIKAS - Oak Ridge Institute For Science And Education (ORISE); VAN GEELEN, ALBERT - Oak Ridge Institute For Science And Education (ORISE); HOANG, HAI - Iowa State University; RADEMACHER, CHRISTOPHER - Iowa State University; YOON, KYOUNG-JIN - Iowa State University; Lager, Kelly

Submitted to: BMC Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2018
Publication Date: 11/20/2018
Citation: Buckley, A., Montiel, N., Guo, B., Kulshreshtha, V., van Geelen, A., Hoang, H., Rademacher, C., Yoon, K.-J., Lager, K. 2018. Dexamethasone treatment did not exacerbate Seneca Valley virus infection in nursery-age pigs. BMC Veterinary Research. 14:352. https://doi.org/10.1186/s12917-018-1693-8.
DOI: https://doi.org/10.1186/s12917-018-1693-8

Interpretive Summary: Foot-and-mouth disease virus (FMDV) causes a vesicular disease in livestock that is recognized as a blister-like skin disease located around the hoof, on the nose, and sometimes in the mouth of cattle and swine. Because FMDV can rapidly spread among livestock it can cause an economically devastating disease that can affect the food supply. Although the United States is free of FMDV, there is constant vigilance for this disease. In swine, sporadic cases of vesicular disease are identified each year that are not caused by FMDV, but are attributed to Seneca Valley virus (SVV) suggesting this virus may be the cause of the disease, and of the FMDV false alarm. Beginning in the summer of 2015 in the United States, there was a dramatic increase of swine vesicular disease cases from which SVV was isolated. This change in the "normal" SVV ecology raised questions. One question was about the potential effect stress might have on causing the upsurge in SVV cases. A study was completed to better characterize how SVV causes disease in swine, as well as look at the effect stress has on this disease since cases often appeared during times of stress such as animal movement. Using a pig "stress model" that used an immunosuppressive drug, "stress" did not seem to enhance the incidence of disease when compared to the SVV only infected group. This finding suggests there may be other changes in the virus and/or current swine production that led to hundreds of SVV cases being reported since 2015. Additional studies are warranted to better understand the ecology of this FMDV look-alike disease.

Technical Abstract: Seneca Valley virus (SVV), a picornavirus, has been infrequently associated with porcine idiopathic vesicular disease (PIVD). In late 2014 there were multiple PIVD outbreaks in several states in Brazil and samples from those cases tested positive for SVV. Beginning in July of 2015, multiple cases of PIVD were reported in the United States in which a genetically similar SVV was also detected. These events suggested SVV could induce vesicular disease, which was recently demonstrated with contemporary US isolates that produced mild disease in pigs. It was hypothesized that stressful conditions may exacerbate the expression of clinical disease and the following experiment was performed. Two groups of 9-week-old pigs were given an intranasal SVV challenge with one group receiving an immunosuppressive dose of dexamethasone prior to challenge to simulate stressful field conditions. Vesicular disease was experimentally induced in both groups with the duration and magnitude of clinical signs similar between groups. During acute infection [0-14 days post infection (dpi)], SVV was detected by PCR in serum, nasal swabs, rectal swabs, various tissues, and in swabs from ruptured vesicles. Virus neutralizing antibody was detected by 5 dpi and lasted until the end of the study. From 15 to 30 dpi, virus was less consistently detected in nasal and rectal swabs, and absent from most serum samples. In conclusion, treatment with an immunosuppressive dose of dexamethasone did not drastically alter the clinical disease course of SVV in experimentally infected nursery aged swine.